Logo: to the web site of Uppsala University

X-ray photoelectron spectroscopy (PES) has been widely applied in the field of battery studies. However, the lack of knowledge regarding the inelastic mean free path (IMFP) for studied systems limits the interpretation of spectroscopic results. In this work, the IMFP of poly(trimethylene carbonate) (PTMC), poly( epsilon-caprolactone) (PCL), and the solid polymer electrolytes consisting of lithium bis(oxalate)borate (LiBOB) together with PTMC or PCL has been determined using PES at a photoelectron kinetic energy of 8.7 keV. Additionally, the surface roughness of these films was investigated by atomic force microscopy and correlated with calculated IMFP values. Our studies reveal that the IMFP of solid polymer electrolytes is higher than that of pure polymers. The presented IMFPs provide references for future spectroscopic studies involving these materials.

The high current-carrying capacity of graphene is essential for its use as an interconnect in electronic and spintronic circuits. At the same time, knowing the breakdown limits and mechanism under high fields can enable new device design strategies. In this work, we push the current carrying capacity of the scalable form of chemical vapor deposited (CVD) graphene employing a high-thermal conducting single crystalline diamond substrate. Our experiments on CVD graphene reveal extremely high current densities > 10⁹ A/cm² in graphene on the diamond with both ohmic (low-resistive) and tunneling tunnel (high-resistive) contacts. Measurements on ferromagnetic (TiO_x/Co) and metallic (Ti/Au) contacts demonstrate current densities of ∼1.16×10⁹ A/cm² and ∼1.7×10⁹ A/cm², respectively. The tunnel (high-resistive) contacts exhibit a shunting of graphene under high currents via the bottom graphitized diamond, resulting in dielectric breakdown and via alternative conducting paths. Electrical measurements show a distinct threshold for conducting paths of graphitized diamond, in tune accordance with Middleton-Wingreen's theory. Our results of high current densities achieved in CVD graphene, with distinct dependence on ohmic and tunneling, contact resistance, and the observed breakdown mechanism, provide new insights for enabling high-current all carbon circuits.

Achieving enhanced and stable electrical quality of scalable graphene is crucial for practical graphene device applications. Accordingly, encapsulation has emerged as an approach for improving electrical transport in graphene. In this study, we demonstrate high-current treatment of graphene passivated by AlOx nanofilms as a new means to enhance the electrical quality of graphene for its scalable utilization. Our experiments and electrical measurements on large-scale chemical vapor-deposited (CVD) graphene devices reveal that high-current treatment causes persistent and irreversible de-trapping density in both bare graphene and graphene covered by AlOx. Strikingly, despite possible interfacial defects in graphene covered with AlOx, the high-current treatment enhances its carrier mobility by up to 200% in contrast to bare graphene samples, where mobility decreases. Spatially resolved Raman spectroscopy mapping confirms that surface passivation by AlOx, followed by the current treatment, reduces the number of sp3 defects in graphene. These results suggest that for current treated-passivated graphene (CTPG), the high-current treatment considerably reduces charged impurity and trapped charge densities, thereby reducing Coulomb scattering while mitigating any electromigration of carbon atoms. Our study unveils CTPG as an innovative system for practical utilization in graphene nanoelectronic and spintronic integrated circuits.

Two-dimensional (2D) van der Waals heterostructures combine the distinct properties of individual 2D materials, resulting in metamaterials, ideal for emergent electronic, optoelectronic, and spintronic phenomena. A significant challenge in harnessing these properties for future hybrid circuits is their large-scale realization and integration into graphene interconnects. In this work, we demonstrate the direct growth of molybdenum disulfide (MoS₂) crystals on patterned graphene channels. By enhancing control over vapor transport through a confined space chemical vapor deposition growth technique, we achieve the preferential deposition of monolayer MoS₂ crystals on monolayer graphene. Atomic resolution scanning transmission electron microscopy reveals the high structural integrity of the heterostructures. Through in-depth spectroscopic characterization, we unveil charge transfer in Graphene/MoS₂, with MoS₂ introducing p-type doping to graphene, as confirmed by our electrical measurements. Photoconductivity characterization shows that photoactive regions can be locally created in graphene channels covered by MoS₂ layers. Time-resolved ultrafast transient absorption (TA) spectroscopy reveals accelerated charge decay kinetics in Graphene/MoS₂ heterostructures compared to standalone MoS₂ and upconversion for below band gap excitation conditions. Our proof-of-concept results pave the way for the direct growth of van der Waals heterostructure circuits with significant implications for ultrafast photoactive nanoelectronics and optospintronic applications.

Two-dimensional (2D) semiconducting dichalcogenides hold exceptional promise for next-generation electronic and photonic devices. Despite this potential, the pervasive presence of defects in 2D dichalcogenides results in carrier mobility and photoluminescence (PL) that fall significantly short of theoretical predictions. Although defect passivation offers a potential solution, its effects have been inconsistent. This arises from the lack of chemical understanding of the surface chemistry of the 2D material. In this work, we uncover new binding chemistry using a sequence-specific chemical passivation (SSCP) protocol based on 2-furanmethanothiol (FSH) and bis(trifluoromethane) sulfonimide lithium salt (Li-TFSI), which demonstrates a synchronized 100-fold enhancement in both carrier mobility and PL in WS₂ monolayers. We propose an atomic-level synergistic defect passivation mechanism of both neutral and charged sulfur vacancies (SVs), supported by ultrafast transient absorption spectroscopy (TA), Hard X-ray photoelectron spectroscopy (HAXPES), and density functional theory (DFT) calculations. Our results establish a new semiconductor quality benchmark for 2D WS₂, paving the way for the development of sustainable 2D semiconductor technologies.